Photooxidative destruction of chloroplasts and its consequences for cytosolic enzyme levels and plant development

Abstract

Mustard (Sinapis alba L.) seedlings were grown in the presence of herbicides (Difunon, Norflurazon) which inhibit carotenoid synthesis without affecting development, in darkness or in continuous far-red light. In strong white light (12,000 lx) the cotyledons of the herbicide-treated seedlings did not contain normal chloroplasts, but only small chlorophyll-free rudiments whose internal structure had almost disappeared. The plastid marker enzyme NADP-dependent glyceraldehyde-3-phosphate dehydrogenase was almost lacking. Plastid ribosomes and ribosomal RNAs were no longer detectable nor could synthesis of mature plastidal ribosomal RNAs be detected. Cytosolic ribosomes and rRNAs were not affected. Plastid DNA was apparently still intact as shown by restriction analysis. The appearance of marker enzymes of glyoxisomes, mitochondria and cytosol was not impaired while the level of marker enzymes of peroxisomes was drastically lowered. Accumulation of anthocyanin in mustard cotyledons was normal after a short, transient delay. Levels of representative enzymes of flavonoid biogenesis (phenylalanine ammonia-lyase, chalcone synthase) were somewhat increased rather than inhibited in the cotyledons of herbicide-treated, white-light-grown seedlings. The growth rate of hypocotyl and cotyledons was inhibited to the same extent in the herbicide-treated, white-light-grown seedling, although light inhibits growth of hypocotyls and promotes growth of cotyledons. Analysis of the data shows that photomorphogenesis of a herbicide-treated, white-light-grown seedling is normal, and is thus independent of plastid gene expression However, a 'factor' which coacts multiplicatively with phytochrome in determining the growth rate of the organs seems to originate from the plastids. Biogenesis of anthocyanin and synthesis of major enzymes of the flavonoid pathway are not affected adversely by a photooxidative elimination of plastid gene expression.

Photooxidative Destruction of Chloroplasts Leads to Reduced Expression of Peroxisomal NADH-Dependent Hydroxypyruvate Reductase in Developing Cucumber Cotyledons

“…We used the herbicide NF (4-chloro-5-(methylamino)-2-(a,a,a-trifluorom-tolyl)-3-(2H)-pyridazinone; Sandoz 9789) to induce photooxidative destruction of chloroplasts in WL (22,24,27). NF inhibits synthesis of carotenoid pigments that protect Chl from photobleaching in strong light.…”

“…NF inhibits synthesis of carotenoid pigments that protect Chl from photobleaching in strong light. In photobleached chloroplasts, Chl content is greatly reduced, as are plastid rRNAs, mRNAs, and proteins (14,20,24). The primary effects of photooxidation are confined to the plastids.…”

Effect of Norflurazon on Resorcinolic Lipid Metabolism in Rye Seedlings

“…These observation confirmed results reporter by Irving and coworkers (1999) who showed that norflurazon significantly increased the elongation growth of etiolated maize coleoptiles in comparison with untreated control. Thus, the effect of this chemical on plants is highly dependent on the light conditions and the differences concern mainly the structure of plastids (Pardo and Schiff, 1980;Reib et al, 1983;Di Baccio et al, 2002). Reib et al (1983) showed that cotyledons of norflurazontreated mustard seedlings grown in strong white light did not contain normal chloroplasts, but only small chlorophyll-free rudiments with completely destroyed internal structure.…”

“…Thus, the effect of this chemical on plants is highly dependent on the light conditions and the differences concern mainly the structure of plastids (Pardo and Schiff, 1980;Reib et al, 1983;Di Baccio et al, 2002). Reib et al (1983) showed that cotyledons of norflurazontreated mustard seedlings grown in strong white light did not contain normal chloroplasts, but only small chlorophyll-free rudiments with completely destroyed internal structure. Treatment of etiolated bean leaves with this herbicide had only little effect on the formation of normal prothylakoids and prolamellar bodies (Pardo and Schiff, 1980).…”

“…The inhibition of carotenogenesis led to a decline in the ratio of ribosomes to plastids, but also affected rRNA synthesis in plastids (Reib et al, 1983). In addition, the expression of many nuclear genes encoding for plastid-localized proteins was suppressed in norflurazon-treated seedlings.…”